1. Field of the Invention
This invention relates to an exposure method and system, and more particularly to an exposure method and system which project light modulated by a spatial light modulator element onto photoresist and expose the photoresist in a predetermined pattern.
2. Description of the Related Art
There have been in wide use a photolithography in production of, for instance, LCDs (liquid crystal display) or TFTs (thin film transistor). The photolithography in production of the TFTs basically comprises a step of coating a thin photoresist layer on a glass substrate having metal film or semiconductor film, a step of exposing the photoresist layer to light through a mask having a predetermined pattern and a step of developing the exposed photoresist layer to form a predetermined resist pattern.
In such a photolithography, reduction of processes is required in order to meet demands for reduction in the cost of LCDs. As an approach of this, there has been known an application of an intermediate tone exposure disclosed in Japanese Unexamined Patent Publication No. 2000-206571. In accordance with this exposure method, an exposure mask which can change the intensity of the exposure light in a plurality of stages in the surface of the exposure mask is employed, and after the development, a resist controlled in its thickness in a plurality of stages according to the pattern can be obtained.
Further, in Japanese Unexamined Patent Publication No. 2002-350897, there is disclosed a method of processing structural members on a TFT panel by the use of the photolithography wherein a plurality of structural members different in thickness are formed on the basis of the intermediate tone exposure.
Further, in “Sharp Technical Report”, No 85, April 2003, pp. 34-35, there is disclosed a structure wherein micro irregularities are formed on the surface of a reflecting member which is formed on a LCD-TFT panel (as substrate material) and is thicker than other light-transmission members, in order to increase the light-scattering function of the reflecting member. Conventionally, such a structure is formed by once forming the reflecting member by the photolithography and then forming micro irregularities on the surface of the reflecting member.
In Japanese Unexamined Patent Publication No. 2004-062157, there is disclosed a method of forming optical circuits laminated on a circuit board in the direction of lamination on the basis of etching by a modulated light beam without use of a photo-mask. In this method, a multiple stages of optical circuits are formed by changing the exposure by the light beam.
The method disclosed in Japanese Unexamined Patent Publication No. 2000-206571 which employs the intermediate tone exposure can contribute to reduction of processes in the photolithography since, by this method, the process which have been done in a plurality of exposures in the usual method where a mask is employed can be done in one exposure.
However, a special mask having slit-like openings spaced at a very small distance from each other is employed in this method in order to realize an intermediate tone exposure. Whereas the pattern accuracy may be ±0.5 μm in the normal mask not for the intermediate tone exposure, a pattern accuracy of not larger than half of the value is required to the special mask for the intermediate tone exposure. Such a high definition mask is very expensive and accordingly, the exposure method employing such an expensive mask is naturally high in cost.
A problem similar to that described above exists in the method disclosed in Japanese Unexamined Patent Publication No. 2002-350897 where a plurality of structural members different in thickness are formed on the basis of the intermediate tone exposure.
Further, in a method where a member is first formed on the substrate material by the photolithography and micro irregularities are formed on the surface thereof as disclosed in “Sharp Technical Report”, No 85, April 2003, pp. 34-35, there is a problem that the method is complicated in structure, which increases the cost of the product.